Sizing paper with a foamed starch



0ct.5, 1965 D. s. READ ETAL SIZING'PAPER WITH A FOAMED ST-ARCH Filed July is, 1965 DRY FOAM SiZE y g TRAP PRESS FOAM LlQUID PINCH FG E c0ce \-FOAM GENERATOR STARCH AND WETTING w y 'j/FOAM 'RECYCLED LIQUID g- LIQUID Q compasssau AIR ' DRY FOAM TRAP F PRESS WE? FOAM FQAM- LlQUlD comsmm mom Fig 2 VALVE --FOAM RECYCLEQ FRESH GENERATOR BY STARCH WETTING smwrrv SOLUTION AGENT A /F0AM uqum Mmmcs I m ZONE INVENTORS:

WAIQPRESSED ooueuxs E. READ WILLIAM B.CRANFORD ANTHONY J. PETRICOLA ATTORNEY list This invention relates to the manufacture of paper having improved surface qualities. More particularly, it relates to a process for improving newsprint, newsroto, novel news, directory, catalog and similar papers.

Many press rooms using newsprint or the like are con- .verting to offset presses. In such presses, the ink, which is considerably more viscous and adhesive than the ink generally used in letterpress printing, is transferred to the paper from a rubber blanket.- An appreciable force is required to remove the printed paper from the rubber blanket, because of the nature of the ink, and such force and the ink cooperate to pick up on the blanket any relatively loose fibers occurring on the surface of the paper and to accumulate such pick-up or lint on the blanket and the printing plate. This ultimately causes a deterioration of the printing quality and eventually forces a shutdown of the press for clean-up. This problem is usually satisfactorily mitigated when the paper is newsprint by doing the offset printing on the wire side of the sheet from which loose fibers are relatively absent, but it is not always possible or convenient to print the wire side of the sheet only and the problem is a significant one with respect to the top-side or felt-side of the sheet.

Accordingly, there is a need to develop means capable of bonding top surface fibers relatively firmly to the main body of a sheet of paper useful in offset printing. These means must be cheap or the economic advantage of using a paper such as newsprint will be lost. In addition, certain deleterious side effects must be avoided. Thus, for instance, since many newsprint offset inks dry mainly by absorption, the porosity of the sheet must be reasonably maintained. Again, since Customs regulations restrict the water penetration resistance of papers which they permit to be imported into the US. duty-free, they practically eliminate the use of rosin size or water resistant film coatings on such papers.

It is, therefore, an object of the present invention to enable the manufacture of the newsprint and other comparable paper stocks having an improved bonding between the top surface fibers and the bodies of such papers simply and inexpensively and with substantially no change in their characteristics of porosity and water penetration resistance. 7

It has heretofore been proposed to apply an uncooked starch to the top suface of a travelling paper web before it is heat dried. See co-pending U.S. Serial No. 178,874, filed March 12, 1962, and now abandoned in favor of continuation-in-part application Serial No. 331,643, filed December 11, 1963. The starch, in the form of an aqueous slurry with or without an admixture of papermakers alum, is not highly viscous and, therefore, does not interfere appreciably with the removal of water from the sheet on, for instance, the wire of a Fourdrinier paper machine. Furthermore, the uncooked starch particles tend to remain near the top surface of the sheet where they are needed, when, upon entering the dryer section of the machine, the combination of heat and moisture causes the particles to swell, become sticky, and to form fiberstarch-fiber linkages which bond the loose surface fibers to the main body of the sheet.

A further refinement is now proposed, one which greatly minimizes the rather large addition of water to the paper sheet which is inherent in the use of a starch slurry the vehicle of which is water and one which, thereby, affords not only greater economy in paper production, but also provides for a more even and better surface sizing of the paper as established by iodine developing. Moreover, such refinement permits the use of minimal quantities of cooked or uncooked starches or mixtures thereof per ton of paper, i.e., about 10 to 20 lbs. of starch per air dried ton of a paper such as newsprint.

In accordance with the present invention, starcheswhether raw, cooked, modified, or any mixture thereof-- are foamed by means of compressed air and with the aid of wetting agents or surfactants; the starch foam is dried by draining and the dried starch foam is applied to the paper sheet (without any submersion or immersion thereof in the foam) by conventional means such as applicator I (1) gm./l. dispersion of an uncooked modified (hydroxyethylated) starch commercially available as SLS 240 (2.) 9 gm./l. sodium lauryl sulfate (an anionic'wetting agent) These were metered to the bottom of a column 2 inches in diameter by 3 feet high. Compressed air was also admitted to the bottom of the column and the resulting foam was led from the top of the column to asmall size press having a nip formed by an upper steel roll and a lower rubber roll. A 15" wide web of newsprint paper was pulled into, through, and out of the size press nip at about 100 fL/min. and, at the same time, the foam was applied to the top roll so as to form a head of foam in the nip between the steel roll and the newsprint. The pumping rates of the two solutions entering the column were regulated so as to coat the web on its felt side with about 15 to 20 lbs. of the starch and about 1.8 lbs. of wetting agent per ton of newsprint. About 15 to 20% moisture was added to the newsprint in the process. The specific volume of the foam was about 20 times that of the liquid giving rise to the foam.

Again, in another example, two aqueous solutions were made up as follows:

(2) 9 gm./l. sodium lauryl sulfate These solutions were employed as were those in the first example. In this case, the rate of application of the starch was about cc./min. and that of the wetting agent was about 60 cc./rnin. Subsequent testing showed the addition to the felt side of the web of about 21 lbs. of starch and the addition of about 24.4% more moisture to the web.

Further work has shown that, in some cases, it is preferable to add some carboxymethylcellulose to the starch to heighten viscosity slightly and to provide a trap in the line from the foaming column to the size press for assistance in drying the foam by draining excess liquid therefrom (the resulting foam is quite stable and is capable of standing in the open atmosphere for several hours with very little liquid drainage). In addition, it has shown that raw starch solutions of 10% or higher concentration can easily be foamed to volume/weight ratios of as high as 50/1 and that cooked starches of up to about 3.3% concentration can be foamed to volume/ weight ratios of about 20/1, a reduction in concentration leading to an increase in ratio. Similarly, mixtures of up to about 3% cooked and about 7% raw starches 

1. IN THE MANUFACTURE OF A PAPER SELECTED FROM THE GROUP CONSISTING OF NEWSPRINT, NEWSROTO, NOVEL NEWS, DIRECTORY AND CATALOG PAPERS, A PROCESS OF BONDING TWO SURFACE FIBERS OF THE PAPER TO THE BODY THEREOF COMPRISING FOAMING STARCH DISPERSED IN WATER BY MEANS OF COMPRESSED AIR AND WITH THE AID OF A WETTING AGENT, DRAINING THE STARCH FOAM TO THE PAPER, AT A RATE EQUIVALENT TO ABOUT 10 TO 20 LBS. PER TON OF AIR DRIED PAPER. 